This column describes a recent Supreme Court case, Clark v. Arizona, in which an adolescent who had schizophrenia was convicted of first-degree murder of a police officer who he believed was a hostile space alien. The Arizona courts had rejected his insanity defense as well as a second defense that he lacked the required intent to commit the crime (mens rea) because his delusions interfered with his knowing that the victim was a police officer. The Court ultimately declined to overturn Arizona's rules regarding the insanity defense and mens rea. However, the column highlights the points in Justice Souter's decision that may have implications for any case involving mental health issues.